Fiber Reinforced Polymer (FRP) Design Example

The following FRP Design example walks the reader through the typical process for designing an FRP strengthening solution for a concrete T-beam per ACI 440.2R Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures.

One of the most important initial checks for an Engineer of Record is to confirm that the unstrengthened structure can support the load combination shown in Equation 5.5.1 in ACI 562 Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings:

Eq. 5.5.1: (φRn)existing ≥ (1.2SDL + 0.5SLL)new

This check is to prevent a structural failure in case that the strengthening is damaged in an extraordinary event. If the structural element cannot pass this check, then external reinforcement is not recommended.

We have a Design Questionnaire where we ask Engineers of Record for more specific information related to the element to be strengthened:

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For this particular example, the following information was provided for the concrete T-beam.

1.  Structure Type (e.g., building, bridge, pier, garage):

  • 5-story commercial concrete building

2. Element(s) to be Strengthened/Repaired (e.g., beam, column, slab, wall):

  • Reinforced concrete beams

3. Type of Deficiency (e.g., shear, flexural, axial):

  • Flexural

4. Existing Factored Capacity of Section (e.g., kips, kip-ft):

  • 265 kip-ft

5. Ultimate Demand to be Supported (e.g., kips, kip-ft):

  • 320 kip-ft

6. Existing Concrete Compressive Strength:

  • 4,000 psi

7. Existing Rebar Yield Strength:

  • 60 ksi

8. Existing Reinforcement Layout:

  • 3 #7s 2.6875 inches from bottom of web to centroid of steel

9. Existing Dimensions:

  • 36 inches total beam height, 8 inches slab, 24 inches web width, 120 inches effective slab width

10. Relevant Existing Drawing Sheets and/or Pictures:

  • See attached

11. Finish Coating Requirements/Preferences:

  • None

12. For Flexural Strengthening:

  1. Dead Load Moment Applied at Time of Installation
    1. 60 kip-ft
  2. Service Dead Load Moment After Installation
    1. 80 kip-ft
  3. Service Live Load Moment After Installation
    1. 140 kip-ft

We then plug this information into our design program to come up with an FRP solution that meets the needs of the member:

masterdoc

For a beam that was at 83% of the capacity required for the new loading, we specified a simple, low-impact FRP solution to maintain clearances under the beams. If a traditional fix of adding cross-section to the beam had been specified instead, then additional concrete and rebar would need to be added to the beam, which would impact clearances under the beam and also increase the seismic weight of the building. The additional weight could also translate all the way through the building and even impact footing designs.

FRP can be used to increase the flexural strength up to 40% per ACI 440.

For your next retrofit project, please contact Simpson Strong-Tie to see if FRP would be an economical choice for strengthening your concrete or masonry element.

Add Simpson Strong-Tie to Your Design Team

Simpson Strong-Tie Composite Strengthening Systems™ is unlike choosing any other product we offer.

For your next retrofit project, please contact Simpson Strong-Tie to see if FRP would be an economical choice for strengthening your concrete or masonry element.


Masonry Reinforcement and Concrete Strengthening with Composites

Guest blogger Brad Erickson, Engineering Manager: Composite Strengthening Systems™
Guest blogger Brad Erickson, Engineering Manager

This week’s post comes from Brad Erickson, who is the Engineering Manager for the Composite Strengthening Systems™ product line at our home office. Brad is a licensed civil and structural engineer in the State of California and has worked in the engineering field for more than 17 years.  After graduating from Cal Poly, San Luis Obispo with a B.S. in Architectural Engineering, he worked for Watry Design, Inc. as an Associate Principal before coming to Simpson Strong-Tie.  Brad is the Engineering Manager for Composite Strengthening Systems and his experience includes FRP design, masonry and both post-tensioned and conventional concrete design.  While not at work, Brad enjoys spending time carting his three kids around to their competitive soccer games and practices.

Have you ever had a concrete or masonry design project where rebar was left out of a pour? Chances are, the answer is yes. Did you wish you could solve this problem by putting rebar on the outside of that element? That’s exactly what Simpson Strong-Tie Composite Strengthening Systems™ (CSS) can do for you and your project. In effect, composites act like external rebar for your concrete or masonry element. Composites can be used in similar configurations to rebar but are applied on the exterior surface of the element being strengthened.

The initial offering in our CSS line is our fiber-reinforced polymer (FRP) product group. An FRP composite is created by taking carbon or glass fabric and saturating it with a two-part epoxy which, when cured, creates the composite. Together, the weight of the fabric and the number of layers in the composite determine how much strength it will add to your concrete or masonry element.

reinforce1 Another form of FRP composite is a precured carbon laminate. The carbon fibers are saturated in the manufacturing facility and are attached to the structure using CSS-EP epoxy paste and filler, an epoxy with a peanut butter–like consistency. We also carry paste profilers (pictured below) that help contractors apply the proper amount of paste to a piece of precured laminate.

reinforce2Of course, before any concrete or masonry reinforcement project can succeed, proper surface preparation is of the utmost importance. Without a good bond with the substrate, a composite will not be able to achieve the intended performance. Concrete voids must be repaired, cracks must be injected and sealed, and any deteriorated rebar must be cleaned and coated. Prior to composite placement, the surface of the substrate must be prepared to CSP-3 (concrete surface profile) in accordance with ICRI Guideline No. 310.2. Grinding and blasting are the most common surface-preparation techniques.

reinforce3The following are just a few applications where composites can be used for concrete and/or masonry retrofits. The orange arrows show the direction of the fibers in the fabric – in other words, the direction in which the composite provides tension reinforcement.

FRP Confinement
reinforce5
Flexural Strengthening
Shear Strengthening
Shear Strengthening
Wall Flexural Strengthening
Wall Flexural Strengthening

This is a summary of the basics of composites and their installation on strengthening projects. As composites are not yet in the design codes in the United States, the American Concrete Institute has produced 440.2R-08: Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures. This guide has numerous recommendations for using fiber-reinforced polymer systems to strengthen your concrete or masonry construction.

If you would like more information about FRP design, you can learn the best practices for fiber-reinforced polymer (FRP) strengthening design during a recorded webinar offered by Simpson Strong-Tie Professional Engineers. We look at FRP components, applications and installation. We also take you behind the scenes to share the evaluation process informing a flexural beam-strengthening design example and talk about the assistance and support Simpson Strong-Tie Engineering Services offers from initial project assessment to installation.

Learn more: Webinar – Introducing Fabric-Reinforced Cementitious Matrix (FRCM)

In this free webinar we dive into some very important considerations including the latest industry standards, material properties and key governing limits when designing with FRCM.

Continuing education credits will be offered for this webinar.
Participants can earn one professional development hour (PDH) or 0.1 continuing education unit (CEU).


For complete information regarding specific products suitable to your unique situation or condition, please visit strongtie.com/rps or call your local Simpson Strong-Tie RPS specialist.

Unreinforced Masonry (URM) Buildings: Seismic Retrofit

Unreinforced Masonry buildings in moderate to high seismic areas can be a disaster in waiting. These types of structures have little or no ductility capacity (reference the recent “Building Drift – Do You Check It?” blog post for a discussion on ductility) required for structures to prevent loss of life in a seismic event. Many of these buildings are in densely populated areas, have historical meaning, and can be costly to retrofit. Fortunately, there are tools available for engineers to assess and design the needed retrofits to mitigate the potential loss of life and increase the seismic resiliency of these buildings.

Image credit: International Code Council (ICC).
Image credit: International Code Council (ICC).

ASCE 31-03, Seismic Evaluation of Existing Buildings, and ASCE 41-06, Seismic Rehabilitation of Existing Buildings, are two reference standards that are referenced in the 2012 International Existing Building Code (IEBC). (It should be noted that both of these reference standards are currently being combined into one document – ASCE 41-13.) Although ASCE 31 and 41 provide assistance to engineers in determining minimum seismic retrofits for these brittle structures, it is recommended that design of the retrofits be performed by a qualified engineer with experience in working with these types of brittle structures.

Currently the 2012 IEBC has been adopted in 39 states in the U.S. and several other areas (see reference map below).

2012 IEBC Adoption Map. Image credit: International Code Council (ICC).
2012 IEBC Adoption Map. Image credit: International Code Council (ICC).

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